Abstract

The aim of this study was to identify the main meteorological drivers of rainfall isotopic variation in north Australia in order to improve the interpretation of isotopic proxy records in this region. An intense monitoring program was conducted during two monsoonal events that showed significant and systematic isotopic change over time. The results showed a close link between isotopic variation in precipitation and variability in monsoon conditions, associated with the presence of large convective envelopes propagating through the study site. The largest negative amplitudes in the isotopic signal were observed when eastward and westward moving precipitation systems within the convective envelope merged over the measurement site. This suggests that the amplitude of the isotopic signal is related to the size and activity of the convective envelope. The strong correlation between rainfall isotopic variation, regional outgoing longwave radiation and regional rainfall amount supports this conclusion. This is further strengthened by the strong relationship between isotopic variation and the integrated rainfall history of air masses prior to arriving at the measurement locations. A local amount effect was not significant and these findings support the interpretation of delta O-18 as proxy for regional climatic conditions rather than local rainfall amount. Meteorological parameters that characterize intra-seasonal variability of monsoon conditions were also found to be strongly linked to inter-seasonal variability of the monthly based delta O-18 values in the Global Network of Isotopes in Precipitation (GNIP) database. This leads to the conclusion that information about the Australian monsoon variability can likely be inferred from the isotopic proxy record in North Australia on short (intra seasonal) and long (inter seasonal or longer) timescales. (C) 2016 Elsevier Ltd. All rights reserved.